Move image transfer code in VMware drivers to OSLO

There is lot of common code between VMware drivers for nova and cinder;
for e.g., session management and VIM API invocation code. The new
VMware driver for glance and the telemetry agent for vSphere are also
planning to use this common code. This change moves methods and classes
for image transfer between VMware servers and the image service into
OSLO.

Change-Id: I033e916a89a89a6adc3cb8e7c9bfb2da626c521b
Implements: blueprint vmware-api